The invention relates to a commercial warewasher for crockery or utensils, which is provided as a box-type warewasher or as a conveyor warewasher, and also relates to a method for operating such a warewasher.
The invention accordingly relates to a warewasher having at least one treatment system comprising a jet system with at least one jet for spraying treatment liquid onto the items to be cleaned within at least one treatment zone.
Warewashers for crockery or utensils according to the invention of this type are either provided as box-type warewashers or as conveyor warewashers.
In particular, conveyor warewashers are flight-type warewashers or rack conveyor warewashers and, in contrast to box-type warewashers, in which the items to be cleaned remain stationary in a single treatment zone of the box-type warewasher during the cleaning process, in the case of conveyor warewashers the items to be washed are transported through various treatment zones of the conveyor warewasher.
A conveyor warewasher normally has at least one pre-washing zone and at least one main washing zone, which is arranged after the pre-washing zone or the pre-washing zones as viewed in the direction of transport of the items to be washed. As viewed in the direction of transport, at least one post-washing zone is generally arranged after the main washing zone or the main washing zones, and at least one final rinse zone is generally arranged downstream of the post-washing zone. As viewed in the direction of transport, once passed through an entry tunnel, the items to be washed either received directly on the conveyor belt or held by racks therefore normally pass through one or more pre-washing zones, one or more main washing zones, one or more post-washing zones and also one or more final rinse zones, a drying zone and also an exit route.
Each of the aforementioned washing zones of the conveyor warewasher is assigned a respective treatment system, which comprises a washing pump and a line system connected to the washing pump, via which washing liquid is fed to the jet system or to the jets of the jet system. The washing liquid or treatment liquid fed to the at least one washing jet of the jet system is sprayed into the respective washing zones of the conveyor warewashers and onto the items to be washed, which are transported through the respective washing zones by a transport apparatus of the conveyor warewasher. Each washing zone is assigned a tank, in which the liquid sprayed by the washing jet is received and/or in which liquid is held ready for the jet system of the respective treatment zones.
In the conveyor warewashers known conventionally from the prior art, final rinse liquid in the form of fresh water is sprayed via the rinsing jets in the final rinse zone onto the items to be washed. At least some of the sprayed final rinse liquid is transported from zone to zone via a cascade system, against the direction of transport of the items to be washed.
The sprayed final rinse liquid is collected in a tank in the post-washing zone, from which it is conveyed via the washing pump of the washing system belonging to the post-washing zone to the rinsing jets of the post-washing zone. Washing liquid is rinsed off from the items in the post-washing zone. The liquid accumulating during this process flows into the washing tank of the at least one main washing zone, which is arranged upstream of the post-washing zone as viewed in the direction of transport of the items to be washed. Here, the liquid is normally provided with a cleaning agent and is sprayed via the jets in the main washing zone onto the items to be washed by means of a pump system belonging to the washing system of the main washing zone. The liquid then flows from the washing tank in the main washing zone into the pre-washing tank in the pre-washing zone. The liquid in the pre-washing tank is sprayed by means of the pre-washing jets in the pre-washing zone onto the items to be washed via a pump system belonging to the washing system in the pre-washing zone in order to remove larger soiling particles from the items to be washed.
Box-type warewashers are warewashers that can be manually loaded and unloaded. These include crockery rack pass-through warewashers, which are also referred to as hood-type warewashers, or front loader warewashers. Front loader warewashers may be undercounter machines, topcounter machines or free-standing front loaders.
A warewasher provided as a box-type warewasher normally has a treatment zone (treatment chamber) for cleaning items to be washed. A washing system provided as a recirculation circuit is generally arranged in this treatment zone. A washing tank, into which liquid from the treatment zone can flow back as a result of gravity, is normally arranged beneath the treatment chamber. Washing liquid, which is normally water, to which cleaning agent can be added as necessary, is located in the washing tank.
The washing liquid located in the washing tank can be conveyed from a washing pump via a line system to the at least one washing jet and, by means of said at least one washing jet, can be sprayed in the treatment chamber onto the items to be cleaned.
In warewashers provided as box-type warewashers, fresh water can be introduced via a fresh water inlet into the treatment chamber, generally into the jet system and line system of the treatment chamber. This is necessary for example at the start of the cleaning program in order to provide a required recirculation quantity of water. After a cleaning program phase of the warewasher provided as a box-type warewasher, introduced fresh water can also be used however as final rinse liquid.
Before new fresh water is fed for final rinsing, the same quantity of washing liquid is generally drained from the washing tank into the on-site wastewater network.
It is already known that the quality of the introduced water is a key prerequisite for an acceptable washing result. Since the water to be introduced is normally removed from the local mains drinking water supply, generally not all requirements of a water quality adequate in terms of washing are met. When assessing the water quality, the overall hardness of the water to be introduced, the chloride content, heavy-metal concentrations and also the total salt content are to be included.
Customary guidelines in the industry for the maximum chloride content in order to avoid pitting in the case of low alloyed cutlery items are 50 mg/l of water for example.
In the case of heavy metals, approximately 0.1 mg of iron and 0.05 mg of manganese/l of water are considered to be maximum values, since an overshoot of these limit values may already lead to a discoloration of the items to be washed and of the warewasher.
Similar considerations apply to the total salt content of the water to be introduced.
In order to observe limit values of this type, it is known to use reverse osmosis systems in commercial warewashers. Commercial warewashers of this type comprising conventional systems for observing water quality limit values of this type have the disadvantage in this case that they are maintenance- and energy-intensive and also produce a large amount of lost water, which can no longer be used for washing purposes. Conventional reverse osmosis facilities therefore require pumps with relatively high pressure and therefore with high delivery rate, such that the energy consumption rises significantly. In addition, the membrane filter systems of reverse osmosis facilities of this type are rapidly blocked, which increases the maintenance costs. In addition, the warewasher is not available for washing operation during the maintenance periods, that is to say in particular during the periods in which the membrane filter systems are replaced.